BCR and chronic myelogenous leukemia, BCR-ABL1 positive: However, the most difficult decision to be taken is when to change therapy in case of “nonoptimal response.” Based on the parameter of a cutoff of 10 %IS BCR-ABL at 3 months, it appears that approximately one third of CML patients do not show an optimal response to imatinib therapy and they are therefore facing a statistically significant higher risk of an inferior outcome in terms of EFS, PFS, and also OS (approximately 80 % at 5 years with respect to >95 % of those below 10 % BCR-ABL at 3 months) [19•, 20–22].